The invention relates to a remote optical gas detection device, which is applicable, in particular, to the monitoring of industrial sites such as chemical plants, refineries, gas storage facilities, etc.
A device of this type is known from documents EP-A-0 544 962 and WO 03/044499, which includes a thermal camera or an infra-red imaging device associated with a measuring filter and a reference filter which, by turns, are placed on the sighting axis of the camera or the imaging device, the measuring filter having a transmission band which includes at least one specific absorption line of a sought-after gas and being sensitive to the presence of this gas, the reference filter having a transmission band comparable to that of the measuring filter but not including the absorption line or lines of the sought-after gas, and therefore being insensitive to the presence of this gas.
The measuring principle consists in using the background of the observed scene as an infrared source and in highlighting the presence of the sought-after gas on the line of sight and in calculating the concentration thereof by differential processing of the infrared images, spatially in order to process the fluxes derived from different temperature points of the observed region, spectrally so as to distinguish the sought-after gas from the background, and temporally to eliminate false alarms and untimely detections.
This device preferably operates in the IR-III band (from 8 to 14 μm), which is broader than the IR-II band (from 3 to 5 μm), and which enables more flux to be absorbed, atmospheric absorption additionally being weaker in the IR-III band than in the IR-II band.
In this known device, the camera used is a cooled camera which is housed in a suitable housing together with the cooling means thereof, and which is connected to a cabinet containing all of the electrical supply means, camera and filter control means and means for processing the signals obtained, this assembly being heavy, bulky and requiring permanent installation.